1. Field of the Invention
The present invention relates to a position-detecting apparatus for detecting a position of an object. Specifically, the present invention relates to a position-detecting apparatus for supplying a fluid from a fluid supply source to a nozzle via an upstream fixed throttle section and jetting the supplied fluid from an end of the nozzle to the object, thereby obtaining a nozzle back pressure.
2. Description of the Related Art
A known position-detecting apparatus generally has a nozzle flapper mechanism or the like utilizing the nozzle back pressure for detecting a position of a workpiece. Such a position-detecting apparatus is shown in FIG. 4. An air passage 2 and a comparing air passage 3 are communicated with an air supply source (fluid supply source) 1. Fixed throttles 4, 5 are disposed in the air passage 2 and the comparing air passage 3.
A detecting nozzle 6 is provided at the end of the air passage 2. The comparing air passage 3 is externally open via a comparing throttle 7 composed of a variable throttle. A differential pressure detector 8 is connected integrally to the air passage 2 and the comparing air passage 3. The differential pressure detector 8 comprises, for example, a diaphragm which is provided in a diaphragm chamber communicating with the air passage 2 and the comparing air passage 3, and a proximity switch which is operated by deformation of the diaphragm (see, for example, Japanese Laid-Open Patent Publication No. 2000-141166).
The air is derived from the air supply source 1 and is branched to flow through the air passage 2 and the comparing air passage 3. The air is supplied to the detecting nozzle 6 and the comparing nozzle 7 via the fixed throttles 4, 5.
The end of the detecting nozzle 6 confronts a surface 9 of an object. The air is jetted toward the surface 9 from the end of the detecting nozzle 6. A nozzle back pressure generates corresponding to the gap between the end of the detecting nozzle 6 and the surface 9. A comparing air pressure generated in the comparing air passage 3 and the nozzle back pressure are introduced into the differential pressure detector 8. It is detected whether or not the surface 9 is located at a predetermined position based upon an obtained result of the detection performed by the differential pressure detector 8.
Another position-detecting apparatus is shown in FIG. 5. An air passage 2a is connected to an air supply source 1a. A fixed throttle 4a is disposed upstream of the air passage 2a. A detecting nozzle 6a is connected to the end of the air passage 2a. A pressure detector 8a for detecting the nozzle back pressure is disposed between the detecting nozzle 6a and the fixed throttle 4a. 
The air is derived from the air supply source 1a and is fed from the fixed throttle 4a to the detecting nozzle 6a. The air is jetted to a surface 9a of an object from the end of the detecting nozzle 6a. A nozzle back pressure generates corresponding to the distance between the end of the detecting nozzle 6a and the surface 9a. The pressure detector 8a detects the nozzle back pressure, thereby detecting the distance between the end of the detecting nozzle 6a and the surface 9a, i.e., whether or not the surface 9a is located at a predetermined position.
Conventionally, the nozzle back pressure can be accurately detected when the end of the detecting nozzle 6, 6a is considerably near the surface 9, 9a. However, no correct nozzle back pressure can be obtained at a position at which the end of the detecting nozzle 6, 6a is relatively spaced from the surface 9, 9a. Therefore, the accuracy of detecting the position of the surface 9, 9a is low.
It is a general object of the present invention to provide a simple position-detecting apparatus which effectively improves an accuracy of detecting a position of a workpiece.
According to the present invention, a fluid is fed from a fluid supply source to a nozzle via a fixed throttle section and is jetted from an end of the nozzle to the object. A nozzle back pressure is thus obtained to detect a position of the object. A diffuser section is disposed downstream of the fixed throttle section.
The fluid supplied to the nozzle via the diffuser section is subjected to energy conversion to be a high pressure fluid, the high pressure fluid being jetted to the object. Therefore, even when the distance (detection position) between the end of the nozzle and the object is relatively large, it is possible to reliably suppress the fluctuation of the nozzle back pressure. It is possible to effectively improve the accuracy of detecting the position of the object with the simple arrangement.
The position-detecting apparatus further comprises a comparing fluid passage. The comparing fluid passage is continuous to the outside of the apparatus from the fluid supply source via another fixed throttle section and which introduces a comparative pressure into a differential pressure detector into which the nozzle back pressure is introduced. The comparing fluid passage has another diffuser section disposed downstream of the fixed throttle section. Accordingly, it is possible to detect the pressure fluctuation in the comparing fluid passage easily and reliably. Further, the differential pressure detector makes it possible to highly accurately detect the position of the object.
The diffuser section is a fluid passage which integrally has a diameter-decreasing section, a straight pipe section, and a diameter-increasing section. Therefore, the arrangement of the diffuser section is simplified, and the desired energy conversion is reliably performed.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.